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MWL#89: Cost-based choice between Materialization and IN->EXISTS transformation

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Fixes for multiple problems/bugs/test failures that resulted from moving
subquery optimization from the execution phase to the optimization phase.
This commit is contained in:
unknown
2010-09-05 18:43:47 +03:00
parent aa195b2570
commit 18ad3bdc2f
14 changed files with 528 additions and 269 deletions
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86
sql/opt_subselect.cc
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@@ -67,12 +67,15 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
{
THD *thd=join->thd;
st_select_lex *select_lex= join->select_lex;
st_select_lex_unit* parent_unit= select_lex->master_unit();
DBUG_ENTER("check_and_do_in_subquery_rewrites");
/*
If
1) this join is inside a subquery (of any type except FROM-clause
subquery) and
2) we aren't just normalizing a VIEW
3) The join and its select_lex object do not represent the 'fake'
select used to compute the result of a UNION.
Then perform early unconditional subquery transformations:
- Convert subquery predicate into semi-join, or
@@ -84,8 +87,9 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
TODO: for PS, make the whole block execute only on the first execution
*/
Item_subselect *subselect;
if (!thd->lex->view_prepare_mode && // (1)
(subselect= select_lex->master_unit()->item)) // (2)
if (!thd->lex->view_prepare_mode && // (1)
(subselect= parent_unit->item))// && // (2)
// select_lex == parent_unit->fake_select_lex) // (3)
{
Item_in_subselect *in_subs= NULL;
if (subselect->substype() == Item_subselect::IN_SUBS)
@@ -129,6 +133,9 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
if (failure)
DBUG_RETURN(-1); /* purecov: deadcode */
}
if (select_lex == parent_unit->fake_select_lex)
DBUG_RETURN(0);
DBUG_PRINT("info", ("Checking if subq can be converted to semi-join"));
/*
Check if we're in subquery that is a candidate for flattening into a
@@ -154,7 +161,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
!join->having && !select_lex->with_sum_func && // 4
thd->thd_marker.emb_on_expr_nest && // 5
select_lex->outer_select()->join && // 6
select_lex->master_unit()->first_select()->leaf_tables && // 7
parent_unit->first_select()->leaf_tables && // 7
in_subs->exec_method == Item_in_subselect::NOT_TRANSFORMED && // 8
select_lex->outer_select()->leaf_tables && // 9
!((join->select_options | // 10
@@ -212,7 +219,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
if (optimizer_flag(thd, OPTIMIZER_SWITCH_MATERIALIZATION) &&
in_subs && // 1
!select_lex->is_part_of_union() && // 2
select_lex->master_unit()->first_select()->leaf_tables && // 3
parent_unit->first_select()->leaf_tables && // 3
thd->lex->sql_command == SQLCOM_SELECT && // *
select_lex->outer_select()->leaf_tables && // 3A
subquery_types_allow_materialization(in_subs) &&
@@ -223,15 +230,27 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
!in_subs->is_correlated && // 5
in_subs->exec_method == Item_in_subselect::NOT_TRANSFORMED) // 6
{
in_subs->exec_method= Item_in_subselect::MATERIALIZATION;
/*
Materialization is possible, later the optimize phase of each
subquery will choose either materialization or in-to-exists based
on cost.
*/
in_subs->exec_method= Item_in_subselect::MATERIALIZATION;
}
else if (in_subs)
{
/* Materialization is not possible at all. */
in_subs->exec_method= Item_in_subselect::IN_TO_EXISTS;
}
/*
Transform each subquery predicate according to its overloaded
transformer.
*/
Item_subselect::trans_res trans_res;
if ((trans_res= subselect->select_transformer(join)) !=
Item_subselect::RES_OK)
{
DBUG_RETURN((trans_res == Item_subselect::RES_ERROR));
}
}
}
DBUG_RETURN(0);
@@ -3505,3 +3524,56 @@ static void remove_subq_pushed_predicates(JOIN *join, Item **where)
}
bool JOIN::choose_subquery_plan()
{
double mat_strategy_cost; /* The cost to compute IN via materialization. */
double in_exists_strategy_cost; /* The cost of the IN->EXISTS strategy. */
bool res;
DBUG_ASSERT(in_to_exists_where || in_to_exists_having);
DBUG_ASSERT(select_lex->master_unit()->item &&
(select_lex->master_unit()->item->substype() ==
Item_subselect::IN_SUBS ||
select_lex->master_unit()->item->substype() ==
Item_subselect::ALL_SUBS ||
select_lex->master_unit()->item->substype() ==
Item_subselect::ANY_SUBS));
Item_in_subselect *in_subs= (Item_in_subselect*)
select_lex->master_unit()->item;
/* Always revert to IN->EXISTS. */
mat_strategy_cost= 1;
in_exists_strategy_cost= 0;
if (mat_strategy_cost < in_exists_strategy_cost)
{
in_subs->exec_method = Item_in_subselect::MATERIALIZATION;
if (in_subs->setup_mat_engine())
{
/*
In some cases it is not possible to create usable indexes for the
materialization strategy, so fall back to IN->EXISTS.
*/
in_subs->exec_method= Item_in_subselect::IN_TO_EXISTS;
}
}
else
in_subs->exec_method= Item_in_subselect::IN_TO_EXISTS;
if (in_subs->exec_method == Item_in_subselect::MATERIALIZATION)
{
// TODO: should we unset the UNCACHEABLE_DEPENDENT flag fro
// select_lex->uncacheable; ?
// This affects how we execute JOIN::join_free - full or not.
// inner_join->restore_plan (keyuse, best_positions, best_read)
;
}
else if (in_subs->exec_method == Item_in_subselect::IN_TO_EXISTS)
res= in_subs->inject_in_to_exists_cond(this);
else
DBUG_ASSERT(FALSE);
return res;
}